During the assembly of engines and turbines, the highly stressed metallic components are provided with ceramic thermal insulating layers in order to protect them from high temperatures. The thermal insulating layers can be applied to the metallic components in a manner, which is the most effective and favorable in terms of cost, by means of thermal spraying, such as, for example, plasma spraying. The ceramic insulating layers, which have been prepared in this way, possess a porous structure which has microscopic fissures running through it, whereby the structure has a reduced modulus of elasticity. As a consequence, the thermal insulating layer can withstand, without damage to a limited extent, the deformations which constantly arise as a consequence of thermo-mechanical stress during operation. However, the ceramic is changed when the thermal insulating layer is exposed to high temperatures exceeding 900.degree. C. Sintering effects arise which lead, as a consequence, to an increased modulus of elasticity. The thermal insulating layer is thus less tolerant with respect to expansion so that the thermo-mechanical stresses lead to so-called segmentation fissures, as a result of which the thermal insulating layer becomes segmented into individual flakes.
In the case of ceramic thermal insulating layers, which have become segmented in this way, simulation calculations and experiments have shown that progression of the fissures toward the interface with the metallic component (metal substrate) occurs during further thermo-mechanical stressing. This progression of the fissures leads to pieces flaking off and hence to the complete failure of the thermal insulating layer.
A process is known from DE 40 41 103 A1 for surface treating structural components by means of shot peening with spherical particles in which a metallic MCrAIY layer is initially applied, in the form of an oxidation layer and hot-gas corrosion layer, to the surface of the structural component and the surface is then shot peened with spherical particles to achieve smoothing of the rough surface of the layer and compacting of the layer. Such a metallic layer is homogeneous and differs fundamentally from a ceramic thermal insulating layer which exhibits grains and grain boundaries.
U.S. Pat. No. 5,277,936 discloses a process for coating a structural component which comprises a basic Ni or Co alloy in which a metallic powder and oxides for the manufacture of a metallic anti-oxidation layer/adhesive surface for a thermal insulating layer are applied by means of plasma spraying. The anti-oxidation layer/adhesive surface is peened in order to achieve compactness. The ceramic thermal insulating layer itself should not be peened.